In a liquid sealed vibration isolating device such as an engine mount, an elastic partition member is provided in a partition member for partitioning a liquid chamber into a primary liquid chamber and secondary liquid chamber, in order to absorb an internal pressure of the primary liquid chamber. A relief valve is integrally provided in an outer circumferential part of the elastic partition member. When the cavitation generating condition where the cavitation is generated in the primary liquid chamber has been created at the time an excessive amplitude vibration such as to generate the cavitation is inputted, the relief valve is opened so as to leak hydraulic liquid of the secondary liquid chamber into the primary liquid chamber, so that the hydraulic pressure of the primary liquid chamber is heightened to thereby prevent the cavitation. This type of the vibration isolating device is known to the public.
FIG. 15 is a plan view of the elastic partition member 100 as referred to above. The elastic partition member 100 is formed in a circular shape and retained in fitting engagement with a rigid part of a partition member. An elastic movable diaphragm 110 is located in a center part of the elastic partition member 100, and a thick rigid frame section 120 is located in the form of a concentric circle in an outer circumference of the elastic movable diaphragm 110 and configured to fix an outer circumferential portion of the elastic movable diaphragm 110. In the radial direction of the elastic partition member 100, a relief valve 130 is integrally formed outwardly of the rigid frame section 120. An opening angle θ of the relief valve 130 in relation to the rigid frame section 120 is constant in the longitudinal direction.
A plurality (four in this example) of relief valves 130 are provided on the outer circumferential portion of the elastic movable diaphragm 110 at proper spaced intervals in the circumferential direction and are easy to bend relative to the rigid frame section 120 by a bending groove 140 which is formed along an outside of the rigid frame section 120 and opened to the primary liquid chamber.
An enlarged part of the drawing is a cross sectional view of a part of the relief valve 130. In this cross section, the relief valve 130 extends radially outwardly from the rigid frame section 120 and obliquely upwardly toward the primary liquid chamber so as to project into a leak passage 150.
The leak passage 150 is a passage which is provided in the rigid part of the partition member for retaining the elastic partition member 100 in an engagement relationship and which provides communication between a primary liquid chamber 170 and a secondary liquid chamber 180. The leak passage 150 is closed when a distal end of the relief valve 130 comes into sealing contact with an inner wall 160 of the leak passage 150, and is opened when the distal end of the relief valve 130 is brought out of contact with the inner wall 160 of the leak passage 150, whereby to provide communication between the primary liquid chamber 170 and the secondary liquid chamber 180. At the time the cavitation generating condition is not satisfied (at the time of the normal condition), the leak passage 150 is closed.
When meeting the cavitation generating condition, since the primary liquid chamber 170 side becomes a negative pressure, the hydraulic liquid within the leak passage 150 pushes up and opens the relief valve 130 from the secondary liquid chamber 180 side so as to create a relief valve opening condition where the hydraulic liquid is leaked and flows from the secondary liquid chamber 180 side into the primary liquid chamber 170, so that the hydraulic pressure of the primary liquid chamber 170 is heightened thereby to prevent the generation of the cavitation.
FIG. 16 is a plan view of the partition member 200. The partition member 200 has a circular rigid member 210 made of metal and the like for supporting the elastic partition member 100 and is formed with an opening portion 220 at a center thereof. An annular fixing section 230 is provided around the opening portion 220, and the rigid frame section 120 is fixed on this fixing section 230. The elastic movable diaphragm 110 surrounded by the rigid frame section 120 is visible through the opening portion 220.
In an outer circumferential side of the fixing section 230, valve openings 240 are formed on a concentric circle of the fixing section 230 at 90° intervals. Each of the relief valves 130 faces the valve opening 240.